National Instruments Network Device DAQ S - Manual (Page 76)

Chapter 7 Counters
NI 6124/6154 User Manual 7-4 ni.com
Controlling the Direction of Counting
In edge counting applications, the counter can count up or down. You can
configure the counter to do the following:
• Always count up
• Always count down
• Count up when the Counter n B input is high; count down when it is
low
For information about connecting counter signals, refer to the Default
Counter/Timer Pinouts section.
Pulse-Width Measurement
In pulse-width measurements, the counter measures the width of a pulse on
its Gate input signal. You can configure the counter to measure the width
of high pulses or low pulses on the Gate signal.
You can route an internal or external periodic clock signal (with a known
period) to the Source input of the counter. The counter counts the number
of rising (or falling) edges on the Source signal while the pulse on the Gate
signal is active.
You can calculate the pulse width by multiplying the period of the Source
signal by the number of edges returned by the counter.
A pulse-width measurement will be accurate even if the counter is armed
while a pulse train is in progress. If a counter is armed while the pulse is in
the active state, it will wait for the next transition to the active state to begin
the measurement.
Single Pulse-Width Measurement
With single pulse-width measurement, the counter counts the number of
edges on the Source input while the Gate input remains active. When the
Gate input goes inactive, the counter stores the count in a hardware save
register and ignores other edges on the Gate and Source inputs. Software
then reads the stored count.